A prison nurse has been found guilty of having an affair with a convicted rapist at one of Britain's highest security jails.

Karen Cosford had sex with inmate Brian McBride, who was serving a life sentence at Wakefield Prison.

She sent the prisoner intimate text messages on a smuggled mobile phone and even wrote him a love letter which was found hidden in a jar of sugar.

Cosford performed a sex act on McBride while she was on duty as two colleagues - Carolyn Falloon and Jacqueline Flynn - guarded his cell, the jury heard. On another occasion, Falloon caught her having sex with the inmate in the medical unit, but failed to report it.

The 47-year-old, of Normanton, West Yorkshire, who worked in the jail's medical centre, denied misconduct, claiming McBride raped her, then bribed and intimidated her so she would not report it. She was also found guilty of failing to tell prison authorities that McBride had a mobile phone, and bringing in top-ups on behalf of the prisoner.

During a trial at Leeds Crown Court that lasted almost four weeks, she said he threatened to kill her and her family if she told anybody about their relationship. But jurors ultimately rejected the claim after hearing how the prison nurse became inappropriately close to the inmate and struck up a sexual relationship which she sustained with gushing text messages.

After supplying mobile phone top-ups to McBride, Cosford texted him telling him he was "dead sexy" and that she loved him. The relationship was exposed when McBride's cell was searched and he told Cosford's husband Darrie, a prison officer, he had been having an affair with his wife.

Falloon, 50, of Wakefield, and Flynn, 46, from Pontefract, were found guilty of failing to report the relationship and not reporting McBride's mobile phone. Falloon was also found guilty of supplying McBride with mobile top-ups. Another of their colleagues, health care officer Kevin Wilson, 56, also of Normanton, earlier pleaded guilty to failing to notify authorities of Cosford's relationship, failing to tell authorities McBride had a mobile phone and supplying McBride with a sim card.

Judge David Hatton QC will sentence Cosford, Falloon and Flynn at Bradford Crown Court on Monday. Wilson, who gave evidence against his colleagues during the trial, will also be sentenced on Monday. All those due to be sentenced were granted bail.

In a statement issued after the hearing, an HM Prison Service spokesman said: "We take any potential staff corruption extremely seriously and will always refer it to the appropriate authorities."